1. Field of the Invention
The present invention relates generally to solid-state light-emitting devices, and more particularly to microcavity semiconductor laser devices for use in an optical information processing system, an optical measurement system, or the like.
2. Description of the Related Art
Recently, solid-state light-emitting devices have been increasingly employed in the field of highly advanced digital computer technology such as an optical communication network, an optical information processing system, or the like. In the field of optoelectronics such as optoelectrical integrated circuit (IC) devices or photonic ICs, it has been studied by those skilled in the art to monolithically integrate semiconductor lasers on a one-chip substrate together with the other types of photosensing elements. Also, to achieve the parallel processing, it has been strongly demanded to integrate lasers in an arrayed fashion on a chip substrate.
A semiconductor laser using a microcavity is expected to be one of the solid-state light-emitting devices most preferably employed in the above applications due to excellent photoemission performance. In the laser of this type, the following two essential processes may exist to obtain output light: spontaneous emission and stimulated emission. The theoretical background thereof is described in, for example, A. Einstein, "Verhandlung der Dcutsche Physicalische Gesellschaft," vol. 18, at p. 318 (1916).
In the systems discussed above, since further improvement in the package density of the devices is strongly required, it becomes necessary to decrease the level of threshold current of each semiconductor laser as low as possible, thereby to improve high-integration fabrication on its monolithic substrate. Unfortunately, the proposed microcavity semiconductor lasers cannot satisfy such requirement of further improvement in the integration density. The reason for this is that the lasers are limited in the coupling ratio .beta. of spontaneous emission to the resonance mode of the microcavity. In other words, the use coefficient of spontaneous emission of the semiconductor lasers remain lower, causing the threshold current level to be higher.